In a WLAN (wireless local area network) system, such as IEEE802.11ac, an 802.11ac BSS (basic service set) can employ spatial diversity technique, DL-MU-MIMO (down-link multi-user multi-input multi-output), to increase its throughput. A high-rate wide band wireless access point (AP) aggregating a plurality of narrow band channels is able to manage wider bandwidth channels and manage wireless stations (STA) of different generations occupying different channel bandwidth. By spatial domain diversity, an 802.11ac AP coalesces one or more narrow channels (20 MHz) into one wide band channel (for example, 160 MHz).
The 802.11ac AP is capable of supporting channels of wider bandwidth, up to 160 MHz. The 802.11ac BSS supports a variety of 802.11 series STAs including legacy STAs (for example, 802.11b/g/n STA) and non-legacy STA (for example, 802.11ac STA).
The bandwidth supported by STAs of an 802.11ac BSS may range from 20 MHz up to 160 MHz. For example, the bandwidth supported by 802.11b/g STA is 20 MHz; the bandwidth supported by 802.11n STA may be 40 MHz; and the bandwidth supported by 802.11ac STA may be 80 MHz or 160 MHz. Therefore, the channel bandwidth available for each MU-MIMO group is gated by the participating STAs with the smallest channel bandwidth
Even though the high-rate wide band wireless environment provides wider bandwidth, the actual channel bandwidth utilized is limited by the STA having the smallest channel bandwidth. As a result, the radio resource is underutilized.
For example, the high-rate wide band wireless access point typically equips with multiple antennas and the multi-user multi-input multi-output (MU-MIMO) scheme is adopted to improve the performance of the wireless network by allowing simultaneous transmissions to a group of STAs. But, in the current MU-MIMO scheme, channels not involved in the current MU-MIMO operation are left un-utilized.
FIG. 1A (PRIOR ART) shows channel bandwidth utilization in the current DL-MU-MIMO scheme. For example, the AP 110 and the STA 121 both support channels 1˜8; the STA 122 supports channel 3; and the STA 123 supports channels 3 and 4. Assuming that the STAB 121˜123 are of the same group. As shown in FIG. 1A, only channel 3 is utilized when the group (including the STA 121˜123) is active. In other words, channels 1˜2 and 4˜8 are unutilized and wasted. So, the radio resource is underutilized.
Further, in coexistence with legacy OBSS (overlap BSS), the 802.11ac AP can not actively manage its channel. FIG. 1B shows that the AP can not actively manage its channel due to in coexistence with legacy OBSS. As shown in FIG. 1B, OBSSs 131 and 132 occupying channel 3 (for example, a channel being 20 MHz) and channels 5˜6 (40 MHz) may prevent the 802.11ac AP from acquiring a wider channel. The 802.11ac AP is capable of coalescing 8 channels to start a BSS, but there are only 2 contiguous channels (40 MHz) available.